Ammonium zirconyl carbonate treatment of chrome-tanned leather



United States Patent 3,551,089 AMMGNIUM ZIRCONYL CARBONATE TREAT- MENT 0F CHROME-TANNED LEATHER William Orval Dawson, Milwaukee, Wis., and Stephen C. OConnor, North Hampton, and Frederick S. Fellowes, Exeter, N.H., assignors to Chemtan Company, Exeter, N.H., a partnership No Drawing. Filed Dec. 7, 1967, Ser. No. 688,666 Int. Cl. C14c 3/06 U.S. Cl. 8-94.27 6 Claims ABSTRACT OF THE DISCLOSURE Disclosed is an improved process of chrome-retanning leather to obtain leather of increased fullness, better softness and increased chrome content. The process comprises treating an initially chrome-tanned leather with a solution of ammonium zirconyl carbonate followed by chrome-retanning.

This invention relates to processes for producing leather from animal hides. More particularly, this invention is concerned with an improved process of producing leather by chrome-retanning.

Large quantities of animal hides are converted into leather. Although cattle hides are the most important raw material for tanners in producing leather, there is a considerable production of leather from calf, sheep, hog and goat hides.

The conversion of an animal hide into leather is done by tanning. Although tanning can be effected by using essentially vegetable materials, and particularly materials which contain appreciable amounts of tannin, such as the bark and wood of oak, chestnut and Wattle, probably a considerably greater amount of leather is produced by the process of chrome-tanning.

Irrespective of the tanning process used, however, the animal hides are usually dehaired. One method of dehairing is to soak the hide in a lime solution containing additives designed to aid in hair removal and to then mechanically remove the hair. The dehaired hides, from which all flesh is removed by scraping, are then treated in a rotating drum with a deliming material such as am monium chloride or ammonium sulfate to neutralize the lime. A pancreatic enzyme is added to the deliming solution to aid in bating and deliming and to further condition the hides. After being washed with water, the hides, after draining, are ready for the tanning process.

In the first step of a conventional chrome-tanning operation, the hides are pickled with a solution of an acid, usually sulfuric acid, and sodium chloride. A chrometanning solution prepared by reducing sodium bichromate in a conventional manner is then introduced into the drum. The drum is rotated during the tanning operation. The basicity of the chrome-tanning solution can vary considerably. Normally, it will be in the range of about 25% to 50%. Furthermore, the conditions of chrome-tanning, such as the volume of the chrome-tanning liquor, the concentration of chromium salts and other ingredients in the liquor and the treatment time are all matters that are well known by those skilled in the art.

Following such a conventional chrome-tanning operation, the hides are sorted according to the use to which the leather ultimately will be put. Subsequently, at least in the United States, the chrome-tanned leather is split. In Europe, however, the leather generally is split after the hair is removed from the hide and before it is bated, pickled and chrome tanned.

In conventional methods of leather production, the chrome-tanned leather insplit form is then treated according to a wide variety of processes to obtain desirable "ice characteristics such as softness, firmness, uniformity of temper, smoothness, grain break and color. Then the leather is fat-liquored, which is essentially the introduction of various water dispersible fats and oils into the leather to preserve and soften the leather.

Although the described general process for producing chrome-tanned leather is suitable for many types of leather production, it is often found that the resulting product lacks the desired softness, fullness and chrome content. Accordingly, to produce leather with these desirable properties and to raise the chrome content, it is common to subject the chrome-tanned leather to a chrome-retanniing process.

In conventional chrome-retanning, the chrome-retam ning liquors used are generally similar to those used in the initial chrome-tanning process. Chrome-retanning as presently practiced is a time-consuming operation and generally leaves considerable to be desired, both in the process and the resulting leather. Most of the time the operation leads to results far short of the desirable fullness, softness and increased chrome content sought in the leather, Furthermore, resistance to shrinkage in the presence of heat, and resistance to perspiration, generally are not improved substantially using conventional chrome-retanning processes. Very seldom can the chrome content of the leather on a dry basis be increased 0.5% to 1% of Cr O by a chrome-retanning operation. Since the initial Cr O content of the chrome-tanned leather on a moisture free basis is in the neighborhood of about 2.5% to 3.5%, it is generally not possible by conventional chrome-retanning operations to produce leather having much over 4.5% Cr O on a moisture free basis.

To overcome the deficiencies of the prior art conventional chrome-retanning processes, there are provided by the subject invention, processes which lead to improved leathers characterized by improved softness, fullness and high Cr O content when a chrome-retanning step is employed in producing the leather.

It has been found according to the present invention that improved chrome-retanned leathers can be produced by subjecting an animal hide previously initially chrometanned by conventional procedures, to the action of ammonium zirconyl carbonate and then to a chrome-retanning solution. The leather resulting from such a process is characterized by a high Cr O, content of up to 5.5% to 6% based on the dry weight of the leather, exceptional fullness and softness as well as improved resistance to heat and perspiration. The chrome-retanned leather produced according to this process can have from about 25% to or more Cr O than conventional chrome-retanned leathers.

The initially chrome-tanned hides are conditioned, according to the invention, for the chrome-retanning operation by contacting the hides with an aqueous solution of ammonium zirconyl carbonate. Ammonium zirconyl carbonate is a liquid under ambient conditions and readily dissolves in water. Although the ammonium zirconyl carbonate solution can contain any suitable amount of this material up to its solubility limit, it is generally advisable to apply a solution containing, on the split and shaved weight of the leather, about 2% (0.2% ZrO to 10% (1.0% ZrO by weight of ammonium zirconyl carbonate with 6% (0.6% ZIO2) being advisably employed. The amount of total solution applied per split and shaved weight of leather is not critical and can vary from about 60% to 300% based on the weight of leather.

In general, as the amount of ammonium zirconyl carbonate employed in the treatment increases, the subsequent absorption of chrome, calculated as Cr O in the chrome-retanning step increases. Accordingly, in practicing this process, one should regulate the amount of ammonium zirconyl carbonate to correlate the quantity used according to the amount of chrome, calculated as C1' O which it is desired to add to the hide by the chrome-retanning operation. Since the ultimate use to which a leather is put will not necessarily require the same chrome increase, calculated as Cr O it is unnecessary in practicing the process to always select conditions which will lead to maximum subsequent absorption of chrome. For example, when an amount of a solution of ammonium zirconyl carbonate is used containing 6.0% (0.6% ZrO by weight of this materal, based on the split and shaved weight of the leather, there can be readily achieved a 2% absorption of Cr O in the chrome-retanning step. When lower Cr O absorption is acceptable, less am monium zirconyl carbonate can be employed. Alternatively, when higher amounts of Cr O are to be introduced into the leather, the ammonium zirconyl carbonate employed should be increased.

To effect the treatment, the hides can be contacted with the aqueous ammonium zirconyl carbonate solution using conventional leather manufacturing equipment such as is employed for chrome-retanning. For example, the chrome-tanned split and shaved leather can be placed in a tanning drum and the solution added thereto. Rotation of the drum brings the solution into intimate contact with all areas of the leather during the process. The solution can be employed at any temperature found suitable for the conditions and equipment although generally the solution should be employed at a temperature of about 70 l30 F. The time of treatment is not considered narrowly critical. The treatment can be continued for such time as is necessary to effect substantial absorption of the zirconium material into the hides. Under normal conditions, this will usually take from about minutes to one hour. Nearly all of the ammonium zirconyl carbonate present in the solution can be absorbed by the leather, unless, of course, an excessive amount of ammonium zirconyl carbonate beyond that which would be reasonably used is brought into contact with the hides. Furthermore, the volume of the ammonium zirconyl carbonate solution is not generally narrowly critical. The volume should, of course, be regulated so that the conventional tanning equipment available can be employed Without any, or a minimum of, change. However, the volume should be sufiicient to achieve ready and thorough contact of the solution with all areas of the leather during the treatment.

During initial contact of the leather with the ammonium zirconyl carbonate solution, the solution Will generally have a pH of about 8.8 because of the basic characteristics of the ammonium zirconyl carbonate. As the treatment progresses and absorption of the ammonium zirconyl carbonate continues, the pH of the liquor drops. It should continue to drop to below pH 7.0, and desirably below pH 6.5, before the treatment is generally considered com pleted.

Under the described conditions of application, it would have been expected that the ammonium zirconyl carbonate would precipitate on the leather producing bad, rather than good, effects. This is because all of the principles of chrome-tanning of leather teach that a basic pH leads to excessively loose breaking leather having an undesirable flat character. The results of processing using ammonium zirconyl carbonate according to this invention surprisingly produce very desirable characteristics in the finished leather rather than the expected undesirable characteristics such as just mentioned. No precipitate of ammonium zirconyl carbonate has been found on leather produced using the process of this invention.

After the ammonium zirconyl carbonate treatment, the leather can be subjected to a normal chrome-retanning operation using conventional chrome-retanning solutions. The basicity of such solutions can vary widely but usually will be about to 60%. A chrome-retanning solution can be used of a volume, and containing an equivalent of Cr O suflicient to supply enough chrome so The following examples are presented to further illustrate the invention.

EXAMPLE 1 Three groups of 100 pounds of chrome-tanned side leather comprising ten sides per group were prepared and subjected to three retanning tests, using one group of sides per test. All sides were split and shaved to 5 02. single. (1 oz. equals 0.4 mm. of leather thickness.)

The retanning tests follow. All percentages are expressed as percentages based on the split and shaved weight of the leather.

TEST 1 The leather was placed in a rotating drum, floated and washed with F. water for 10 minutes and then the water was drained.

The leather was floated in 7.5 gallons (60% by weight) of water at 80 F.

Four pounds of an acidic liquid exchange tannin was added and the drum rotated for 10 minutes. The liquor was pH 3.5.

To the leather was then added 4.4 lbs. of zirconium silica sulfate followed by rotation for 20 minutes. The liquor was at pH 2.20. One pound of calcium formate was added dry and the drum rotated 20 minutes. The liquor was pH 3.10.

To the leather was added 3 lbs. of wattle bark extract spray dried and 3 lbs. of dry clay and the drum rotated 20 minutes. The liquor was pH 3.05.

The leather was floated with water and washed 5 minutes at 130 F., the water drained and the leather floated with 7.5 gallons of water at 130 F.

The leather was fat liquored using 11 lbs. of a sulfated sperm oil-flour mix and 3 gallons of water at 130 F. with rotation of the drum for 20 minutes.

The leather was then finished with topping oils at pH 3.33, the leather cooled with water at 80 F., washed With 65 F. water for 5 minutes and pull and horse smoothed.

The exchange tannin liquid, the zirconium silica sulfate and the 'wattle bark are all tanning materials which are capable of converting hide substance to leather. They do not contain chromium compounds. The zirconium silica sulfate is normally included with the other tanning materials because it increases the fullness and produces firmer and tighter breaking leather.

i TEST 2 The leather was floated and washed in a drum 10 minutes in water at 120 F., the water drained, and the leather refloated in 7.5 gallons of water at 120 F.

To the rotating drum was added a solution of 6 lbs. of ammonium zirconyl carbonate, containing the equivalent of 0.6 lbs. ZrO- diluted with 1.5 gallons of water at F. The drum was rotated 30 minutes. The liquor was pH 6.85. The leather had a pH of 5.50, inside out and a pH of 6.80, outside cut.

The drum was drained of liquor, the leather floated in 7.5 gallons of water at F., 2% Cr O as a 48% basic chrome liquor was added and the drum rotated one hour. The liquor was pH 3.85. The exhaustion of the chrome from the liquor was very good and estimated to be 95%.

The liquor was drained from the leather, the leather floated in 7.5 gallons of Water at 85 F., 3 lbs. of wattle bark (dry) and 3 lbs. of dry clay added. The drum was rotated and 4 lbs. of an acidic liquid exchange tannin diluted with 1.5 gallons of water at 120 F. was added.The drum was run 30 minutes. The liquor was pH 3.55.

The leather was floated with water and washed 5 minutes at 130 F. The leather was then fat-liquored and finished with topping oils as in Test 1.

TEST 3 The procedure of Test 2 was followed except that 1 lb. of sodium formate was used with the ammonium zirconyl carbonate solution to raise the internal pH of the leather. The inside pH of the leather was 6.5 and the outside pH of the leather was 6.8 after this part of the treatment.

RESULTS TABLE l.DRY CRUST EVALUATION OF LEATHER Uniformity of temper Average Average break temper 1 Good No good 2. 30 3. 12 1 side 9 sides. 2.27 2. 73 7 sides. 1 side. 2.10 2 66 8sides D0.

1 The lower the number the better on a 1 to 5 scale.

The results of Table 1 show Tests 2 and 3 by comparison with Test 1, or the control system, produced an improved leather having a tight break, a uniform mellow temper, a good layout and good fullness. The leathers of Tests 2 and 3 were definitely fuller both by feel and gauge than the leather of Test 1. Test 1 leather was poorest for layout while Tests 2 and 3 leathers had a good layout.

STAKING EVALUATIONMOIST After the leather was dampened back to about 28% moisture, the leather was check for necessary staking or mechanical softening.

Test l.All ten sides had to be head and shoulder staked or mechanical softened.

Test 2.Only two of the ten sides had to be head and shoulder staked.

Test 3.-No sides had to be staked.

STAKING EVALUATION-DRY The leather was temper sorted for further evaluation with the results given in Table 2.

The leathers of Tests 2 and 3 were obviously softer than the leather of Test 1.

A stratographic analysis was made for chrome, calculated as Cr 0 in the leather. The results are given in Table 3.

The results show the leathers of Tests 2 and 3 have approximately twice the amount of chrome than does the leather of control Test 1. The chrome values for Test 1 are essentially the chrome content of the initial chrome tanned leather since the retanning of Test 1 introduces no chrome.

The leathers were also evaluated after being buffed and the results are given in Table 4.

TABLE 4 Test 1 Test 2 Test 3 Average break 2. 26 2. 27.. 2.22. Average temper 3.04"". 2. 73 2.73. Uniformity:

Good 1 side-.- 6 sides--. 5 sides;

Fair 3sides. 3sides..- Do.

Poor fisides 1 On a scale oil to 5 with the lower number indicating better break or temper.

The results showed little difference in break. The leathers of Tests 2 and 3 are softer and much more uniform in temper than Test 1 leather.

EXAMPLE 2 Two groups of pounds of chrome-tanned side leather comprising nine sides per group were prepared and subjected to two retanning tests. The sides were split and shaved to 5.25 02. single.

The retanning tests, and dry leather evaluations follow. All percentages are expressed as percentages of the split and shaved weight of the leather.

TEST 1 The leather was placed in a drum and floated and washed in water at F. for 6.5 minutes. The water was drained and the leather floated in 60% by weight of water at 120 F.

To the rotating drum was then added, as an aqueous solution, 6% by weight of the leather of ammonium ziroconyl carbonate, containing the equivalent of 0.6% ZrO diluted in 10% by weight of Water at 120 F. The drum was rotated 20 minutes. The pH of the liquor was 7.0. The liquor was found to be very well exhausted of ammonium zirconyl carbonate.

To the rotating drum was added 1.5% by weight of Cr O as a 48% basic chrome liquor (1 gallon). The drum was rotated one hour. The exhaustion of the chrome from the liquor was estimated at 95%.

The leather was then washed, colored and fat-liquored according to a standard procedure.

TEST 2 This test was a control. It was the same as Test 1 except that no ammonium zirconyl carbonate was employed. Following the chrome-retanning, the sides were piled out overnight and neutralized and washed the next day. Coloring, fat-liquoring and finishing were as in Test 1.

The leather of Test 1, after drying, was found to be more mellow than the leather of Test 2 and much more uniform in temper.

The Test 1 leather was definitely tighter and softer than the Test 2 leather.

The Test 1 leather was approximately 0.25 oz. heavier (1 oz. equals 0.4 mm. in leather thickness) in single gauge thickness than the Test 2 leather.

On a hide substance basis, the Cr O content of the Test 1 leather was 8.08% and of the Test 2 leather was 6.86%.

The ash on the Test 1 leather was 11.32% and on the Test 2 leather was 8.14%.

The Test 1 leather had a pH of 3.73 and the Test 2 leather a pH of 3.29.

The stratagraphic analysis for percentage chrome, as Cr O on a hide substance basis is given in Table 5.

TABLE 5 Percent ClzOa Test 1 Test 2 Flesh slice I Average;

The foregoing detailed description has been given for clearness of understanding only, and n0 unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.

What is claimed is:

1. In the process of chrome-retanning leather, the improvement which comprises contacting a leather to be chrome-retanned with an aqueous solution of ammonium zirconyl carbonate containing the equivalent of about 0.2% to 1% ZrO based on the weight of the leather, at a temperature of about 70 to 130 F. until the pH of the solution goes to about 7 or lower to eflect absorption of the zirconyl component into the leather, and then chrome-retanning the leather with about a 25 to 60% basicity chrome-tanning liquor.

2. The process of claim 1 in which the leather is initially chrome-tanned with about a 25 to 50% basicity chrome-tanning liquor befor it is contacted with the ammonium zirconyl carbonate solution.

3. The process of producing leather from a cattle hide which comprises:

dehairing, batting and deliming and pickling the hide in preparation for tanning;

giving the hide an initial chrome-tanning using a chrome-tanning liquor having a basicity of about 25 to contacting the initially chrome-tanned hide with an aqueous solution of ammonium zirconyl carbonate containing the equivalent of about 0.2% to 1% ZrO based on the weight of the hide, at a temperature of about to F. until the pH of the solution goes to about 7 or lower;

chrome-retanning the hide with about a 25 to 60% basicity chrome-tanning liquor; and

fat-liquoring the hide.

4. The process of claim 3 in which the hide is split after the initial chrome-tanning and before treatment with the ammonium zirconyl carbonate solution.

5. The process of claim 3 in which the hide is split after dehairing and before the initial chrome-tanning.

6. The process of claim 3 in which the hide is contacted with the ammonium zirconyl carbonate solution at least until the pH of the solution drops below pH 6.5.

References Cited UNITED STATES PATENTS 1,940,610 12/1933 Somerville 8--94.25X

- OTHER REFERENCES Blumenthal: Zirconium ChemicalsTheir Application to Textiles-Part I, Rayon and Synthetic Textiles, December 1950, pp. 81-83.

GEORGE F. LESMES, Primary Examiner J. R. MILLER, Assistant Examiner U.S. Cl. X.R. 8-94.25 

